Conventionally, thread cutters associated with cutting machines have a straight blade that exposes approximately a 1/8 inch cutting surface which, when dulled, has to be replaced, meaning machine down-time and increased servicing costs. While there have been proposals (i.e., see U.S. Pat. No. 1,312,659) for circular cutting blades, such cutting blades do not entirely solve the problem since it is necessary to loosen and rotate the circular cutting blade upon the dulling of an edge thereof, and since the cutting blade must be replaced once the entire peripheral edge thereof has been dulled.
According to the present invention, a thread-cutting assembly associated with the sewing machine is provided that has an extremely long life time compared to the prior art cutting devices, yet may be readily and safely mounted on various sewing machine parts so that thread cutting can be accomplished with a minimum waste of thread. The cutting disk according to the invention is automatically sharpened during use thereof and rotates upon engagement of work therewith so that a sharp cutting edge is always presented.
According to the present invention, a thread-cutting assembly is provided comprising a circular disk having a circumferential cutting edge, guard means for preventing access to the majority of the circumferential cutting edge of the disk but exposing a portion of the disk circumferential cutting edge, means for mounting the disk to the guard means so that the disk rotates with respect to the guard means about an axis when thread to be cut by the disk is brought into engagement with the exposed portion thereof so that a new cutting surface is exposed, and means for operatively mounting the guard means to a sewing machine. The guard means comprises means for sharpening of the disk cutting edge upon rotation of the disk with respect thereto, the guard means being formed of a metal having a greater temper than the metal of which the cutting disk is formed. The guard means includes a plate having a depression formed therein concentric with the axis of rotation of the disk, and the peripheral portions of one face of the disk engage the plate while the rest of the disk does not engage the plate. The mounting means for the disk simply comprises a threaded opening in the guard plate, a bore in the cutting disk, and a screw having a shoulder portion that prevents locking of the disk to the plate, the screw defining the axis of rotation of the disk.
The cutting assembly may be associated with any convenient mounting location of the sewing machine; for example, the disk may be mounted for rotation about a horizontal axis and operatively connected to an arm connected to a garment-holding foot of the sewing machine.
It is the primary object of the present invention to provide a safe, long-life thread-cutting assembly that always presents a sharp cutting surface. This and other objects of the invention will become apparent from an inspection of the detailed description of the invention and from the appended claims.